1. Field of the Present Invention
The present invention relates to a transducer access control system for use in a disk recording/reproducing apparatus for moving a transducer a required distance from its present position over a disk in the radial direction thereof, and more particularly, to a transducer access control system providing highly reliable rapid rough access using reference velocity data which varies relatively to the distance moved by transducer.
2. Description of the Prior Art
In general, rough access and precision access control systems are applied in devices for recording and playing back data from a disk-type recording medium provided with data tracks formed either concentrically or spirally in a radial direction. Each track is divided into multiple sectors which are the smallest access unit. Rough access is executed to move the transducer into the vicinity of the target position and is followed by a precision access, locating the transducer at the final target position. Rough access drive may be accomplished by a linear motor or other device. Furthermore, if the rough access is accomplished with high precision and reliability, the access time for the precision access can be reduced, resulting in the reduction of the total access time.
Furthermore, acceleration and deceleration with conventional rough access control is accomplished by time referencing. However, there is a limit to the precision which can be obtained with acceleration/deceleration control using time referenced control.
Furthermore, when the velocity of the transducer is detected, the periods between the output pulses from the scale are counted and the velocity is calculated from this count. There is, therefore, a delay in the control response equivalent to the time required for the calculations to be performed.
Thus, a transducer access control system designed to resolve these and related problems is proposed, for example, in Japanese Patent Application No. 62-113383 assigned to the same assignee as the present application. Proposed in this application No. 62-113383 is a system provided with a transducer which records data to and reads data from a recording medium, a travel signal generating device which generates a travel signal corresponding to the travel of the transducer and a velocity detection means which detects the travel velocity of the transducer. A counting device counts the output from the travel signal generating device and a median position detection device detects the median value of the access distance based on the count obtained by the aforementioned counting device. A reference velocity generating device generates a triangular velocity pattern (FIG. 6) which gradually increases the reference velocity during the first half of the rough access operation and gradually decelerates the reference velocity during the later half of the rough access operation. A comparison device compares the reference velocity generated by the reference velocity generating device with the travel velocity detected by the velocity detection device, and a drive device adjusts the travel velocity of the transducer based on the comparison result of the comparison device. This system uses the relationship between the physical position data of the transducer and the velocity data of the transduce as to accomplish the rough access with good precision by providing reference velocity data.
However, in the aforementioned access control system, as shown in FIG. 6, the reference velocity is outputted from the reference velocity generating device in such a manner that the velocity increases in the first half to median point 603, at which point a maximum velocity is reached, and then decreases in the later half from median point 603 in a so-called "triangular control" system, and thus, efficient, high speed access at the maximum capacity of the drive means is not possible.